Most photographers start out as “generalists”, i.e. taking pictures of a wide range of subjects. I think there is nothing wrong with it, in principle, but most experts agree that from a business standpoint, it is good to choose niche and specialize in it. Actually, this is true for any business, not just photography.
Finding a niche is important because there is only so much time in a single lifetime, and developing the skills specific to a certain genre is a long process. In fact, one can argue that development of a skill is an endless journey. Unfortunately, skills and expertise often do not cross over between different niches. For example, the techniques, the equipment and the entire approach that are required for macro photography are completely different from those used in sports or fashion niches.
There is also a question of marketing. It is easier to promote a portfolio if it is focussed on a single topic.
Having said this, I personally find that focussing on a single niche to the exclusion of all other types of photography would be a sure way to kill the enthusiasm that made me pick up the camera to begin with. Thinking more philosophically, perhaps there is a certain contradiction between “focus” and “balance” in a general sense. If you intensely focus only on one aspect of your life, other areas inevitably suffer.
In kendo, which I believe is a metaphor for everything else in life, there is a concept of tokui waza – a special, favourite technique, which has the highest probability of success. Tokui waza is specific to a particular kendoka, who strive to identify what their best technique is and then focus their practice on polishing this special skill. However, this specialization cannot be done at the expense of other techniques. Otherwise, the range of available skills/techniques would become so narrow, that an experienced opponent would be able to exploit it as a weakness.
I think the answer is in the degree of focussing. Ideally, I would like to specialize in a given area just enough, so that the result would be legitimate expertise without unwanted side effects. Paraphrasing the term popularized by Tim Ferriss, it is the minimum effective dose (MED) of focussing – the smallest amount of focus that would produce the desired outcome, beyond which, focussing is ineffective or even harmful.
If we agree that specializing, to some extent, is beneficial, choosing a niche in photography is not trivial (as I mentioned, most of us start as generalists), so I will leave this subject until another post.
